Tijuana defeated Toluca 2-1 on Thursday in the first leg of Mexico's first division final and has the edge going into Sunday's deciding match in Toluca.
Fidel Martinez and Paraguayan Pablo Aguilar scored in the first half for Tijuana, with the second goal allowed despite replays suggesting he was offside. Edgar Benitez scored for Toluca.
Tijuana is a newcomer to Mexico's first division and was promoted only last year, while Toluca is attempting to win its 11th title to equal Guadalajara Chivas as Mexico's most successful club.
Tijuana had deservedly taken the lead in the 24th minute when Martinez brought down a pass chipped over the defense by Cristian Pellerano and slotted the ball through goalkeeper Alfredo Talavera's legs and into the net.
The hosts dominated the first half and had a number of half chances, but Toluca equalized two minutes later with its first real attack of the game.
Paraguayan Benitez scored from a tight angle when Lucas Silva slid the ball across goal after a mistake by US international Edgar Castillo sent him through down the right.
Aguilar tapped in Tijuana's second in the 40th minute after US international Joe Corona flicked on a freekick swung in from the right by Fernando Arce.
Replays showed Aguilar was slightly offside, sparking protests from Toluca players and manager Enrique Meza at halftime.
Tijuana had the better of the possession and play in the second half, but the game became largely a midfield battle and was a much tighter affair.
Over the 90 minutes, Tijuana had eight shots on target compared to Toluca's two.
Toluca went into the final as slight favorite and finished as leaders in the regular-season standings, but a draw in the second leg is good enough to see Tijuana crowned champion.
''We are happy, we fought to the end like always,'' Tijuana's Colombian striker Duvier Riascos said. ''The team gave its all to get an important result and thanks to God we achieved it.''
With only a one-goal deficit to overcome, Benitez said his side can snatch the title in the second leg, saying: ''We've got to be calm, look for the goal and to control the game.''
The Mexican season is divided into two halves - the Apertura season - the one now underway - and the Clausura season starting in January. Each crowns its own champion.
